(a) What do you meant by an Expert System (ES) and explain briefly the essential differences between a Decision Support system and ES.

(b) What are decision tables and what are they used for? Provide suitable examples of limited and extended tables, as well as the use of the ELSE rule.

(c) You work for an IT call centre which responds to user queries relating to their PC. Currently a spate of computer virus's have infected PC's with the following characteristic:

If the user is getting an error message showing that the system will re-boot in N seconds and then the system actually does re-boot THEN the user must install an operating system update and obtain virus software to clean the virus.

In addition, IF the user cannot connect to the internet, as they get the "line busy" error, THEN they must re-install their ISP connection software as well.

Produce a limited entry decision table to model the above rules. You should then produce a second table, which removes any redundant vertical rules resulting in the same decision.